Within the class of apparatus that has such a free hanging pendulum arrangement are cutting machines typically provided with a plurality of cutting elements and adapted for cutting vegetation, for example at a desired height above ground level so as to avoid cutting short grass or other desirable plants which are shorter than other undesirable plants such as relatively tall weeds. Another type of apparatus of interest is a spraying machine having a plurality of spraying heads and adapted for spraying plants with such as chemicals etc. for example pesticides, herbicides and the like.
Various boom arrangements have been described in many documents, such as in International Application no. PCT/IE02/00097 (WO 03/005799), which is to the present inventor. The arrangement described includes a boom which is pivotally mounted to a pendulum arrangement. The arrangement described by the present inventors in that document is an important one, as it is necessary to ensure that the boom is provided in a stable operating condition such that the vehicle can traverse different terrain conditions without altering the performance of the functionality of the boom for example cutting or spraying. Generally the arrangement described in that document works well to maintain the boom in an orientation generally parallel to the plane of the surface over which the vehicle carrying the apparatus passes. This is particularly important for sloped or uneven terrain.
When a delicately balanced apparatus such as that described in the various embodiments of PCT/IE02/00097 is disrupted from its balanced position, such as by disruptive forces imparted to any part of the apparatus which forces disrupt the boom and/or pendulum position from the natural (equilibrium) position (determined by gravity), it may take a short while for the apparatus to dissipate the disruptive force (e.g. through unwanted boom and/or pendulum movement), during which time the boom may remain in an undesired position, or possibly reciprocally move about (and past) a desired position.
A major cause of such disruptive forces are those imparted by irregular surfaces over which the vehicle is passing e.g. when a wheel of a vehicle passes over a rut, hole or depression in the surface causing the vehicle to lurch to one side and back again, —both actions disrupting the natural position of the boom and in cases where a substantial shock force is imparted a severe rocking of the boom to one side can occur. The boom can then undergo an undesirable see-saw action. This action can cause the boom to catch the vegetation over which it passes and in cases of severe disruptive forces may cause the boom to catch the ground. This means that the boom does not operate at a desired height above the ground and this affects the action carried out by the boom, for example spraying or cutting. For example the whole of the vegetation may not be sprayed because at least a part of the boom is too low, or if cutting, the boom may be too high on one side to cut, and cut too low down on the other side thus cutting into desired vegetation which should not be cut.
While the present inventor has described in PCT/IE02/00097 mechanisms for alleviating this problem there is still a need to provide a stabilising system for such an agricultural apparatus against such disruptive forces.
An additional problem that presents itself whenever a boom of relatively large span is utilised, is prevention of straining/bending out of shape of the boom due to encountered resistance forces. This is a difficult task particularly where the boom is to be free to move under gravitational forces. Typically the resistance forces arise in two circumstances—the first due to the boom catching on something, e.g. catching a fence, gate post, hedge or becoming entangled in vegetation being part of a crop or otherwise; and the second due to its own inertia e.g. the moment it experiences about a fulcrum point when the vehicle carrying it changes velocity, for example by a sharp increase in speed or due to turning the vehicle relatively sharply.
There is also a need to protect such a boom from being damaged by such resistance forces. It will be appreciated by those skilled in the art that the boom could be bent out of shape by such forces.
Furthermore when a large span boom such as that described above is in its working or floating position it can be difficult to maintain the boom in a desired orientation relative to the ground or vegetation over which it passes. The system (for example as described in the above referenced International application) allows the boom to move transverse to the direction of travel of the tractor in what could be described as a floating position. The system is very effective in the operating position however there are times when the system can be difficult to control. An example of this is when the machine is working in a field with a slope, turning at the end of the run or headland to work back in the opposite direction. A lot of adjustment is required and this can be quite slow because of the floating nature of the boom and system.
For example if working on the side of a hill where one side of the vehicle is lower on the slope of the hill than the other, turning on the hill to work back along the field parallel to the portion of the field just worked (a previous pass), will involve a large amount of adjustment of the boom angle, as the angle of the boom will need to be reversed to allow movement of the boom along the field in an opposing direction. For example, if the boom is angled at say 30° to the horizontal with a left arm or side of the boom at a lower position and a right side or arm of the boom at a higher position in order to allow working on the side of a hill, then, to reverse direction, the boom will generally have to be reversed so that the right arm or side is lower and the left side is higher. In the example given (where the slope of the hill is the same for the next pass) the boom will have to be moved through 60°, to be tilted at 30° in the opposite way. Such adjustment may have to be done by an operator while turning on a headland of a field. This adjustment can be difficult particularly while at the same time the vehicle must be turned to make the next parallel pass in the opposing direction.